diff --git a/tools/lib/string.c b/tools/lib/string.c
index bd239bc..a4246f1 100644
--- a/tools/lib/string.c
+++ b/tools/lib/string.c
@@ -39,27 +39,45 @@ void *memdup(const void *src, size_t len)
  * @s: input string
  * @res: result
  *
- * This routine returns 0 iff the first character is one of 'Yy1Nn0'.
- * Otherwise it will return -EINVAL.  Value pointed to by res is
- * updated upon finding a match.
+ * This routine returns 0 iff the first character is one of 'Yy1Nn0', or
+ * [oO][NnFf] for "on" and "off". Otherwise it will return -EINVAL.  Value
+ * pointed to by res is updated upon finding a match.
  */
 int strtobool(const char *s, bool *res)
 {
+	if (!s)
+		return -EINVAL;
+
 	switch (s[0]) {
 	case 'y':
 	case 'Y':
 	case '1':
 		*res = true;
-		break;
+		return 0;
 	case 'n':
 	case 'N':
 	case '0':
 		*res = false;
-		break;
+		return 0;
+	case 'o':
+	case 'O':
+		switch (s[1]) {
+		case 'n':
+		case 'N':
+			*res = true;
+			return 0;
+		case 'f':
+		case 'F':
+			*res = false;
+			return 0;
+		default:
+			break;
+		}
 	default:
-		return -EINVAL;
+		break;
 	}
-	return 0;
+
+	return -EINVAL;
 }
 
 /**